Mobile communication device such as cellular phones and portable information terminal equipment are widely spread with the developments in the information-oriented society. For example, the cellular phones use RF bands as high as 800 MHz˜1.0 GHz and 1.5 GHz˜2.0 GHz. In order to cope with such RF bands, duplexers using acoustic wave filters such as surface acoustic wave (SAW) filters or film bulk acoustic resonators (FBARs) are used.
Japanese Patent Application Publication No. 2006-203149 discloses an electronic device in which an acoustic wave filter that is flip-chip mounted on an upper surface of a package substrate is sealed with solder or the like. Japanese Patent Application Publication No. 2009-296508 discloses a duplexer in which a package substrate composed of multiple layers stacked is used and a transmission acoustic wave filter and a reception acoustic wave filter, which are flip-chip mounted on an upper surface of the package substrate, is sealed with solder or the like.
Recently, the cellular phones have made further progress in multiband and multimode and have become increasingly sophisticated. For example, the cellular phones are equipped with an auxiliary wireless interface such as wireless local area network (LAN) or global positioning system (GPS). In the above situation, there is an increasing demand for reduction in the size and height of the duplexer.
In order to reduce the height of the duplexer, it is considered to thin the package substrate. A thinned package substrate may be realized by thinning each layer thereof. In this case, patterns formed on the layers become closer to each other. For example, a transmission line provided on a layer may be electromagnetically coupled with a metal formed on another layer. Similarly, a reception line provided on a layer may be electromagnetically coupled with a metal formed on another layer. Thus, a signal leakage may occur between the transmission and reception lines via the metals, and the isolation characteristic between the transmission and reception lines may deteriorate.